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If this is true. It's just staggering to me. If there was life on Mars.... there may still be. If there was life on Mars, then how common is life elsewhere in the galaxy? If it can exist on ancient Mars, there's no reason it can't exist on any of the other millions of planets scattered through the billions of stars in our Galaxy.

If life is found on Mars... or found to have existed.... then it can be anywhere.

Under the ice of Europa aswell?

While we may never meet our neighbours..... it would still be nice to know that yes, they may well be out there.... somewhere. The Galaxy may well be teeming. I sure hope it is. I mean, if it becomes clear that rather than being just blacks, whites.... whatevers.... on a cosmological scale where there is actual non-terrestrial life.... shouldn't it be clear that we all are just the one race?

Can someone explain to me why the set of meteorites are considered more likely to have originated on Mars than from an impact on Earth itself?

Are there Earth-origin ones known to distinguish them from, since debris from such an earth impact would more likely have orbits intersecting earth's, or is some other evidence used? I'm having trouble finding it.

As a iochemist, it was my understanding that the habitable zone was already known to extend out toward Mars. Although really, I'd say that the concept of a habitable zone needs to be expanded anyway considering the possibility of life in the Jupiter system. I believe that it is becoming increasingly clear that there isn't just a single habitable zone around a star like our sun but also pockets of habitable space underneath the surface of various moons and terrestrial planets like Mars.

I think Mars was already considered habitable range. We know that billions of years ago Mars was warmer and wetter, and if it was a little more massive, so it could better hold an atmosphere, it might still be. All this is true regardless of whether or not Mars once had life.

As a iochemist, it was my understanding that the habitable zone was already known to extend out toward Mars.

Well. there's a difference between being potentially habitable for a species, and finding remnants of actual life. Either life appear on both Earth and Mars independently, meaning there's actually a quite wide band of possible conditions - or life really transports across space. Either way is much more compelling arguments for the habitable zone actually being habitable than a theoretical zone based on temperature.

Humankind's only hope is the development of a hyper-drive (a. k. a. warp-drive) engine based on the science discovered by Burkhard Heim.

Nonsense. Such a drive would still take us too long to get to another world. It would take us minutes perhaps even hours which we don't have. We already know that's too long! We must use the power of sarcasm to move without moving! That way we don't have to consider anything remotely difficult at all.

More seriously, even with chemical propulsion, the worst case, you can get to Mars in about six months. Sure it's a hard problem, but that's all that it is. There's nothing impossible about getting to Mars. It would be nice to have some far faster means of getting there, but it's not necessary.

It could be hit and miss. Just because fossil evidence got here doesn't mean anything living made the trip. But, it does open up a lot of questions. If the Mars microbes didn't make it, that doesn't mean something else didn't. We'll figure it out in a few centuries,...

Actually, astronomers figured it out a few decades ago. They concluded that, while the Mars -> Earth trip is difficult and unlikely, the other direction has happened with probability around 0.999999.... The mechanism is the Earth's "dust tail", a stream of gases and dust much like a comet's tail, but even thinner. It is thick enough to cause a problem for some astronomical observations, though, which is why some astronomers studied it during the 1960s and 70s. They found that the tail includes "dust" as large as bacteria, and since high-altitude airplane and balloon samples had shown bacteria at all altitudes, our default assumption should be that there are bacteria (mostly in spore form) in our planet's dust tail. This wouldn't be a million-year trip. The solar wind blows Earth's dust tail outward along the plane of Earth's orbit. It would sweep over each of the outer planets about once per year, contaminating each planet with bacterial spores in each pass.

So if we find life on any outer planet that is chemically similar to bacteria here, we can't conclude anything about where it originated, except that the most likely source is Earth. It could have reached Earth from the outside, of course, and is just making the return trip.

A fun part of these studies was the conclusion that this thin stream of bacterial spores does eventually get blown out of the solar system. Distances out there are large, of course, but if you look at the numbers, you find that the Earth takes roughly 4 trips around the galaxy every billion years. Since the earliest known bacterial life developed here, we've made 15-20 trips around the galaxy, spewing bacterial spores along our path the whole time. Chances are that they've pervaded the entire galaxy (very, very thinly). If they can survive the millions or billions of years in interstellar space, then we're one of the sources for the panspermia hypothesis.

Of course, the astronomers didn't know anything at all about the survivability of bacterial spores in space. We still don't know much about it. That's the weak link in the whole guessing game.

But it's highly likely that there are bacteria living underground on Mars, and they came from Earth. It would be a lot more fun if we found some there whose biochemistry was different from the micro-organisms on this planet.

(I googled for this topic a couple of years ago, and didn't find much of anything. I wonder if there are any astronomers here who could point us to more details.)

Humans are generally considered a form of advanced life and we've transported ourselves and microbes across space. The thing I don't understand is why it's such a wild and crazy concept to consider the possibility of advanced life traversing space from Mars to Earth millions or billions of years ago.

Either way is much more compelling arguments for the habitable zone actually being habitable than a theoretical zone based on temperature.

If it isn't already, the habitable zone should be stratified into layers indicating habitable for humans down to microbes. Some people are only interested in discussing habitable for humans while others think more expansively. Thinking in layers would clear up any confusion.

And you were able to deduce all this from the presence of a "worm-like" object associated with a meteorite?

No. It's from various studies of Mars. It's had almost a dozen successful orbiters and 5 successful landing vehicles on it. There is plenty of evidence that Mars was once much wetter.

It also comes from knowledge of Earth. Our atmosphere and water is largely protected from space radiation due to our magnetic field, which based on commonly-accepted theories is generated from currents within Earth's semi-liquid-metal core. The field acts as a radiation shield.

Bigger planets take longer to cool. Mars, being about half the diameter of Earth cooled off much quicker, it's core now almost solid (or at least stationary). All planets and large moons had a hot core at one point in time soon after formation, and thus probably also had a magnetic field (assuming sufficient metal content). The difference is in part how fast the core cools, which is largely a function of body mass. (It's expected that Earth's magnetic field may give out in a couple of billion years.)

In fact, Mars' ancient magnetic field left slight magnetic patterns in rocks, almost like tape-recorder tape, which can be detected from orbiters. This tends to confirm that Mars once had an ample magnetic field also, explaining how all that water was able to stay on the surface. A thick enough atmosphere allows water to stay liquid and not evaporate into space via ionization.

Also, the cratering rate of the solar system has been estimated and modeled from studies of the moon. Based on these rates, one can estimate the age of various larger-scale surface features of Mars using crater density. If you know the rate of bombardment throughout history, you can estimate the age of surface features. It's sort of like estimating the age of a car by looking at the pebble nicks on the front bumper.

Sure, it could all be wrong, but it's the model that currently best matches the evidence: Mars used to be "nice".

I wonder, though. If Jupiter is the solar system's vacuum cleaner, eliminating much of the deadly debris that might destroy Earth, then wouldn't it also act in the same with with panspermia dust from Earth?

[If] life on Mars and life on Earth share a common history, it makes it much easier to muck around on Mars, because it'll just be another extension of life here so no worry about contamination.

That may not be a safe assumption. When Earth organisms go into new environments on other parts of Earth, they often encounter microbes they are not accustomed to, and become ill or die. It could be a big risk.

If ANY life on Mars is found, regardless of origin, it may be best to leave it alone. Send only one-way labs or colonies to Mars. Don't risk the sci-fi Andromeda Strain [wikipedia.org] come real.

He's saying if all life in the solar system came from the same source, it will all look essentially the same (with overall minor variations). I'll be more specific, so you can understand the analogy.

Suppose you toss a bucket of yellow paint in five directions, making five splashes on the ground. One may land on concrete, and look completely different from the one that landed on grass, which looks totally different than the one that landed on the bush, etc. But when you take a sample of what they are all made of, you'll find they are made of exactly the same stuff: yellow paint.

For a car analogy, suppose there are five models of vehicle in existance. They are very different, some are bigger and tougher, others are smaller and faster, etc. If they were all made at a GM factory, though, then they are similar at the fundamental level - they are all made with the same type of steel, rubber, and plastic, and they have similarities in design across the board.

That's what he's talking about when he talks about all life coming from the same source. It makes it seem less likely that the rest of the universe will be teaming with life if we find that it only happened once to our solar system. In truth, the chances don't change at all, it just seems different. There could just as well be cans of red, or blue, or white paint, as well as fords and toyotas and hondas out there. We already know it can happen once, the chances that it can happen again don't really change whether it happened once and migrated across our solar system or if it happened several times in our solar system, or if it only ever happened once in our solar system. It doesn't do anything for the likelihood of life in a completely separate system.